1.Field of the Invention
The invention relates to a metallic joining material with components of nickel and chromium.
2.Description of the Prior Art
Such a metallic joining material finds application particularly for joining parts of oxide-precipitation-hardened alloys. Parts for forming rotor and stator blades as well as heat-retarding segments of gas turbines are preferably joined together with this joining material. Complex parts of oxide-precipitation-hardened alloys cannot be cast. They must be joined together from two or more parts to form a final part. Forming parts of oxide-precipitation-hardened alloys starts with the preparation of the powder forming the alloys. The metals and metal compounds which are employed in the preparation of the powders are mechanically alloyed in a high-energy mill. From the powder obtained in this manner, base bodies are first made by extrusion. The base bodies are subsequently processed further by forging, rolling and/or mechanical processing to form parts. The latter are then joined together by means of metallic joining materials, for instance, via a high-temperature soldering process to form rotor and guide blades or other parts, for instance, for gas turbines.
A metallic joining material, under the designation TD6, which consists substantially of 16% by weight chromium, 4% by weight silicon, 5% by weight tungsten and 17% by weight molybdenum and nickel, the remainder being nickel is known. Another joining material which is commercially available under the designation AMDRY 400, consists of 16.5% by weight nickel, 19% by weight chromium, 0.8% by weight boron, 8% by weight silicon and 4% by weight tungsten, the remainder being chromium. A third joining material with the designation AMDRY 788, contains 21% by weight nickel, 22% by weight chromium, 2% by weight boron, 2% by weight silicon, 14% by weight tungsten. The remainder consists of cobalt. These commercially available joining materials do not meet the requirements demanded of them. The high-temperature corrosion resistance required for turbine applications can be met only by an increased alloy content of equal to or more than 16% chromium as well as contents of Ti and aluminum. The aluminum required for the formation of an oxidation-resistant cover layer is present in none of the known solder alloys to a sufficient degree (.gtoreq.4%). Since high silicon contents result in increased danger of brittle phase formation on the basis of the known phase diagrams NiCrSi, such as the sigma phase and boron content of equal to or less than 2% lead to a heavy undesired incipient dissolution of the base material, the Si content should be limited to .ltoreq.4% and the boron content to .ltoreq.2%. However, these concentrations should not be made substantially smaller because thereby, the melting point of the solder is set. The joining materials with too high a refractory content, especially too high a tungsten, molybdenum and tantalum content are frequently not compatible with protective layers.